The invention relates to an exhaust line for an internal-combustion engine, which exhaust line contains a catalyst and a bypass pipe bypassing the catalyst. The bypass pipe can be shut off by way of a shut-off valve having a diagnostic capability. The invention further relates to a shut-off valve with the diagnostic capability.
To provide an emission control that is as extensive as possible, it is desirable with respect to catalysts contained in an exhaust line of an internal-combustion engine that the diameter be small and the cell number be high. For reasons of power, particularly for not building up an exhaust back pressure that is too high, a large diameter and a low cell number are advantageous.
For at least partially resolving this conflict, exhaust lines, particularly those having several catalysts, are equipped with a bypass pipe bypassing at least one of the catalysts. Under defined operating conditions, this bypass pipe can be shut off by way of a shut-off valve so that, under these operating conditions, all exhaust gas flows through all catalysts, whereas, under other operating conditions, a portion of the exhaust gas flows through the bypass pipe and thereby bypasses the catalyst around which the flow takes place.
It is an object of the invention to further develop an exhaust line of the above-described type such that the shutting-off of the bypass pipe can be diagnosed; that is, it can be determined by way of a diagnosis whether all exhaust gas is in fact flowing through the exhaust line or the catalyst(s) present in the exhaust line.
According to the invention, an exhaust line for an internal-combustion engine contains a catalyst and a bypass pipe bypassing the catalyst, which bypass pipe can be shut off by way of a shut-off valve. The shut-off valve has a diagnostic device for diagnosing a tightness of the shut-off valve.
Advantageous further developments of the exhaust line according to the invention are described and claimed herein.
It is a further object of the invention to provide a shut-off valve which has a simple construction, is capable of reliably diagnosing its tightness, and can be used particularly for the exhaust line according to the invention.
From German Patent document DE OS 25 32 838, a shut-off valve is known by which it is to be prevented that media, mutually separated by the shut-off valve, mix with one another in conduits of pipes. This shut-off valve has two valve seats spaced in the flow direction of the medium flowing through them when the shut-off valve is open. The shut-off vale also contains a valve stem to which one valve disk is rigidly mounted and another valve disk is mounted so that it can be moved against the force of a spring. By operating the valve stem, the valve disks can simultaneously be caused to rest against the valve seats. The space between the valve seats can be flushed by use of a liquid fed from the outside and through a gap between the valve stem and the valve disk movably guided on the valve stem.
From German Patent document DE OS 2 262 727, a shut-off valve is known which can be used particularly for gas burning systems and contains two valve seats spaced in the flow direction of the medium flowing through them. Further, two mutually concentrically arranged valve bodies are provided, which can be displaced relative to one another and, in a closed position, each rest sealingly against one of the valve seats. A diagnostic space is formed between the valve seats or the valve bodies and is accessible from the exterior by way of a diagnostic pipe, this diagnostic pipe being the only access to the diagnostic space when valve bodies rest sealingly against the valve seats. By the action of vacuum on the diagnostic pipe, it can be determined whether the valve closes reliably in that, for example, in the case of a given output of a vacuum pump within a predetermined time period, a predetermined vacuum is reached or a reached predetermined vacuum decreases by less than a predetermined value within a defined time period.
According to the invention, a shut-off valve is provided in the case of which two valve bodies are rigidly connected with a valve stem and tolerances are compensated such that at least one of the valve seats, while having a sealing effect, is movably held on the housing of the shut-off valve.
Further advantageous embodiments of the shut-off valve according to the invention are described herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.